US8699546B2 - Blind detection of modulation configuration for interfering signals - Google Patents
Blind detection of modulation configuration for interfering signals Download PDFInfo
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- US8699546B2 US8699546B2 US13/452,399 US201213452399A US8699546B2 US 8699546 B2 US8699546 B2 US 8699546B2 US 201213452399 A US201213452399 A US 201213452399A US 8699546 B2 US8699546 B2 US 8699546B2
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
- H04B1/69—Spread spectrum techniques
- H04B1/707—Spread spectrum techniques using direct sequence modulation
- H04B1/7097—Interference-related aspects
- H04B1/711—Interference-related aspects the interference being multi-path interference
- H04B1/7115—Constructive combining of multi-path signals, i.e. RAKE receivers
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
- H04B1/69—Spread spectrum techniques
- H04B1/707—Spread spectrum techniques using direct sequence modulation
- H04B1/7097—Interference-related aspects
- H04B1/7103—Interference-related aspects the interference being multiple access interference
- H04B1/7107—Subtractive interference cancellation
Definitions
- the present invention generally relates to wireless communications receivers, and more particularly relates to techniques for determining the modulation formats and channelization codes used by interfering radio signals.
- both the uplink (mobile terminal-to-base station communications) and downlink (base station-to-mobile terminal communications) are subject to various sources of interference, including, for example, intra-cell interference arising from a lack of complete orthogonality between user signals within a wireless system cell, inter-cell interference arising from signals intended for users or originating from users in other cells, and thermal noise.
- interference cancellation techniques are increasingly being deployed.
- decoder interference cancellation IC
- post-decoder interference cancellation One category of interference cancellation techniques is known as decoder interference cancellation (IC) or post-decoder interference cancellation.
- IC decoder interference cancellation
- the general idea behind decoder interference cancellation is that a signal generated using decoder output from a first decoding attempt is subtracted from the input signal before a second decoding attempt.
- the decoder output from the first decoding attempt could relate to an unwanted signal, for the purpose of cancellation.
- FIG. 1 illustrates an example of an interference cancelling receiver 100 that uses output from a decoder to perform interference cancellation.
- This receiver system is sometimes referred to as a Turbo interference cancellation receiver.
- a so-called RAKE receiver is shown, which indicates a Wideband Code-Division Multiple Access (W-CDMA) application of decoder interference cancellation.
- W-CDMA Wideband Code-Division Multiple Access
- the output of the decoder 140 produces log-likelihood ratios (LLR), which are essentially estimated probabilities that the corresponding decoded information bits should be set to one or zero.
- LLR log-likelihood ratios
- the LLRs are used by soft mapper 150 to generate the symbol values that were most likely to have been transmitted by another node, such as a base station when the receiver is in a wireless terminal.
- An estimate of the received signal corresponding to these symbol values is produced by signal regenerator 160 , which applies the same modulation and scrambling that was removed from the signal by RAKE despreader 110 and demapper 130 in the first decoding iteration.
- the regenerated signal from signal regenerator 160 is subtracted from the original input signal, using subtracter 105 , to produce an interference-reduced signal.
- the contribution to the despread signal from the original received signal (for a given code) is denoted y k (i) and the contribution from the subtracted signal is denoted as ⁇ tilde over (y) ⁇ k (i), where i is the symbol index and k the channelization code.
- An equalizer illustrated as a G-RAKE combiner 120 in FIG. 1 , applies equalizer weights to the despread signal to reduce the effects of multipath propagation.
- the resulting equalized, despread, symbol samples are then demapped, by demapper 130 , to convert them from soft symbols to soft bits.
- decoding is performed by decoder 140 , which produces a new (and improved) set of probabilities (LLR) for the transmitted bits.
- LLR new (and improved) set of probabilities
- HSDPA High-Speed Downlink Packet Access
- HS-PDSCH High-Speed Physical Downlink Shared Channel
- identifiers for other wireless terminals (user equipment, or UEs, in 3GPP terminology) in the vicinity of a wireless terminal of interest are known, then it is possible to decode scheduling messages sent to these UEs via High-Speed Shared Control Channel messages. These scheduling messages carry information that at least partly defines the channelization codes and modulation schemes to be used in subsequent HS-PDSCH transmissions to that UE.
- the UE identifier for the targeted UE is used to mask the HS-SCCH messages, which makes it necessary to know the UE identifier to properly decode the HS-SCCH message.
- a receiver knows the UE identifiers for neighboring UEs and is thus able to successfully decode HS-SCCH messages corresponding to interfering HS-PDSCH transmissions, some obstacles remain.
- One problem is that the HS-SCCH message cannot be interpreted properly unless the receiving unit knows whether the UE targeted by the HS-SCCH has been configured to support 64-QAM operation. This configuration is performed through signaling at higher layers, and it is nearly impossible for a UE other than the one targeted by the configuration message to intercept it.
- a UE eavesdropping on HS-SCCH messages intended for other UEs is still unable to determine the channelization codes and modulation schemes used for HS-PDSCH messages to those UEs from the contents of the HS-SCCH alone. Without knowledge of the channelization codes and modulation schemes used for the interfering HS-PDSCH transmissions, the UE is unable to decode and regenerate the interfering signals as needed to perform interference cancellation.
- U.S. Patent Application Publication No. 2010/0260231 describes a method for blind detection of a transport format of a signal, and discloses techniques for reducing the number of transport format hypotheses to be considered in the blind detection. Additional techniques are needed to determine the channelization codes and modulation scheme for interfering HS-PDSCH transmissions.
- the actual channelization codes used for the HS-PDSCH depend on whether or not 64QAM configuration has been signaled to the target wireless terminal. Accordingly, techniques are needed for determining which channelization codes are used for an interfering HS-PDSCH transmission without knowing whether the UE targeted by that transmission has had its 64QAM capability activated by higher layer signaling.
- this is accomplished by measuring the amplitude on each of several possible groups of channelization codes for each of one or more nearby UEs that might be the targets of interfering HS-PDSCH messages. Testing to see whether the amplitude is approximately the same across the codes in a possible combination of channelization codes yields a metric value that indicates whether that particular combination of codes is likely to be transmitted to a given UE. A second metric that detects the most likely modulation for possible groups of channelization codes is also calculated. The two metrics are combined to determine which combination of channelization codes and modulation scheme is most likely being used for addressing a UE in the vicinity of an interference-cancelling receiver.
- An example method begins with the reading of downlink order data for each of one or more neighboring wireless terminals from a downlink control channel.
- the downlink order data specifies an assignment of one or more channelization codes and a modulation scheme for the corresponding neighboring wireless terminal, where each assignment depending on the downlink order data and an unknown modulation configuration parameter previously sent to the corresponding neighboring wireless terminal.
- the downlink order data is read from an HS-SCCH scheduling message targeted to the neighboring wireless terminal and the unknown modulation configuration parameter is the 64QAM configuration status of the wireless terminal.
- a code-power consistency metric is then calculated for each of the neighboring wireless terminal.
- This code-power consistency metric indicates the probability that all of the channelization codes corresponding to the wireless terminal in a given combination are transmitted with the same power, and is based on despread data samples corresponding to the channelization codes for the respective wireless terminal, given the channelization code allocation for the combination under consideration.
- the code-power consistency metric for each of the neighboring wireless terminals is further based on a filtered average of values for the unknown modulation configuration parameter determined from previous most likely combinations.
- a modulation-matching metric is calculated for each of the neighboring wireless terminals, for each of the possible combinations. Again, this modulation-matching metric is based on received despread data samples corresponding to the channelization codes. The modulation-matching metric indicates how closely the received symbols match a constellation pattern for one of the possible modulation schemes.
- the modulation-matching metric for each of the neighboring wireless terminals for a given possible combination is calculated, for each neighboring wireless terminal and its corresponding channelization codes, by comparing despread samples for the corresponding channelization codes to an assumed map of constellation points and calculating a fraction of despread samples that fall outside defined windows centered on each constellation point.
- the modulation-matching metric corresponds to the most likely modulation scheme for the wireless terminal, given a possible allocation of channelization codes. In other cases, however, the modulation-matching metric for each of the neighboring wireless terminals is calculated based on assumed modulation schemes for each of the neighboring wireless terminals, where the assumed modulation schemes are determined from the current assumed values for the unknown modulation configuration parameter.
- the technique summarized above is of particular use in an interference-cancelling receiver, as the channelization code and modulation scheme information can be used to demodulate traffic data transmitted to the neighboring terminals, e.g., HSDPA transmissions in an HSDPA system. Accordingly, the operations summarized above may in some cases be followed by the forming of a reconstructed estimate of interfering signals corresponding to one or more of the neighboring wireless terminals, based on corresponding channelization codes and modulation schemes determined from the most likely one of the possible combinations. Interference cancellation can then be using the reconstructed estimate.
- a modulation configuration detection circuit configured to carry out one or more of these techniques.
- This modulation configuration detection circuit might be used, for example, to augment an interference-cancelling receiver, thus enabling the receiver to regenerate and cancel interfering signals targeted to neighboring wireless terminals.
- One embodiment of such a modulation configuration detection circuit includes a HS-SCCH message decoder, which reads and interprets downlink assignment messages for neighboring wireless terminals.
- the downlink order data included in these messages specify an assignment of one or more channelization codes and a modulation scheme for the targeted wireless terminal, but the proper interpretation of the order data depends on whether or not the wireless terminal is configured for 64QAM operation, which is normally unknown to other receivers.
- the modulation configuration detection circuit further includes a hypothesis generator, which identifies all possible combinations of channelization codes and modulation schemes for all of the neighboring wireless terminals, taking into account possible values for the unknown modulation configuration parameter and that no two wireless terminals are assigned the same channelization codes.
- a metric generator calculates two metrics for each of the neighboring wireless terminals, for each possible combination: a code-power consistency metric and a modulation-matching metric. These metrics are based on despread data samples corresponding to the channelization codes for each wireless terminal, for each possible combination of channelization code and modulation scheme allocations. Detailed examples of these calculations were given above. Finally, a channelization code and modulation identifier identifies a most likely one of the possible combinations, using a weighted sum of the code-power consistency metrics and modulation-matching metrics for each possible combination. This information is supplied to demodulation circuits so that the corresponding HS-PDSCH transmissions to the neighboring wireless terminals can be demodulated, regenerated, and cancelled from the received signal.
- a modulation configuration detection of the sort summarized above can be implemented in a processor circuit configured with software instructions for carrying out one or more of the detailed techniques disclosed herein.
- This processor circuit can be combined with other receiver circuits, such as in an interference-canceling receiver.
- still further embodiments of the invention include a receiver circuit configured to identify channelization codes and modulation schemes for interfering signals targeted to neighboring wireless terminals.
- the receiver circuit in several of these embodiments includes a despreading circuit configured to generate despread data samples for each of a plurality of channelization codes and a demodulation and decoder circuit configured to decode downlink order data from a downlink control channel, for each of one or more neighboring wireless terminals.
- the receiver circuit in these embodiments further includes a processing circuit configured to read the corresponding downlink order data for each of the one or more neighboring wireless terminals, the downlink order data specifying an assignment of one or more channelization codes and a modulation scheme for the corresponding neighboring wireless terminal, each assignment depending on the downlink order data and an unknown modulation configuration parameter previously sent to the corresponding neighboring wireless terminal.
- the processing circuit is further configured to identify all possible combinations of channelization codes and modulation schemes for all of the neighboring wireless terminals, taking into account possible values for the unknown modulation configuration parameter and that no two wireless terminals are assigned the same channelization codes and to calculate a code-power consistency metric for each of the neighboring wireless terminals, for each possible combination, based on despread data samples corresponding to the channelization codes.
- the processing circuit is also configured to calculate a modulation-matching metric for each of the neighboring wireless terminals, for each possible combination, based on received despread data samples corresponding to the channelization codes and to identify a most likely one of the possible combinations, using a weighted sum of the code-power consistency metrics and modulation-matching metrics for each possible combination.
- FIG. 1 is a block diagram illustrating an example interference cancelling receiver.
- FIG. 2 illustrates the constellation pattern for QPSK modulation.
- FIG. 3 illustrates the constellation pattern for 16QAM modulation.
- FIG. 4 is a process flow diagram illustrating an example method according to some embodiments of the present invention.
- FIG. 5 is a process flow diagram illustrating another example method according to some embodiments of the present invention.
- FIG. 6 is a block diagram illustrating functional components of a modulation configuration detection circuit according to some embodiments of the invention.
- FIG. 7 illustrates an example processing circuit.
- radio access network that communicates over radio communication channels with wireless terminals (also referred to as user equipment, or “UEs”). More particularly, specific embodiments are described in the context of systems using Wideband Code-Division Multiple Access (W-CDMA) technology and/or High-Speed Downlink Packet Access (HSDPA) technology, as standardized by the membership of the 3 rd Generation Partnership Project (3GPP). It will be understood, however, that the present invention is not limited to such embodiments and may be embodied generally in various types of communication networks.
- W-CDMA Wideband Code-Division Multiple Access
- HSDPA High-Speed Downlink Packet Access
- mobile terminal can refer to any device that receives data from a communication network, and may include, but are not limited to, a mobile telephone (“cellular” telephone), laptop/portable computer, pocket computer, hand-held computer, and/or desktop computer.
- cellular mobile telephone
- laptop/portable computer laptop/portable computer
- pocket computer pocket computer
- hand-held computer hand-held computer
- desktop computer desktop computer
- base station which may be referred to in various contexts as NodeB, for example
- wireless terminal mobile terminal
- wireless device often referred to as “UE” or “User Equipment”
- UE User Equipment
- base station e.g., a “NodeB”
- UE User Equipment
- the suppression and/or removal of interfering signals is fundamental to improving the coverage and throughput of advanced wireless systems.
- cancelling of interfering HS-PDSCH transmissions is particularly beneficial.
- the interference-cancelling receiver must be able to decode the interfering HS-PDSCH transmissions, which means that it must know the codes used to spread and scramble the signals as well as the modulation schemes used to map the transmitted data to the signals.
- the interference-cancelling receiver can obtain some of this information by intercepting and decoding scheduling messages sent to the targets of the interfering signals, which are carried in High-Speed Shared Control Channel (HS-SCCH) transmissions.
- HS-SCCH High-Speed Shared Control Channel
- HS-SCCH messages are masked, using an identifier for the target UE.
- an identifier for the target UE In the discussion that follows it is assumed that a list of potential UE IDs in the neighborhood of the UE is already known.
- Several approaches for learning the identity of neighboring UEs are described in co-pending U.S. patent application Ser. No. 13/291,900, filed on 8 Nov. 2011 and titled “A Method and Apparatus for Identifying Other User Equipment Operating in a Wireless Communication Network,” the entire contents of which are incorporated herein by reference.
- the known UE identifiers are used to test whether a transmission to any of them is scheduled in any given transmission time interval (TTI).
- TTI transmission time interval
- the first slot of the three slot HS-SCCH transmission i.e., the HS-SCCH Part 1 message
- the first slot of the three slot HS-SCCH transmission i.e., the HS-SCCH Part 1 message
- the parameters carried by the HS-SCCH Part 1 message specifically identify the codes to despread, as well as a parameter to indicate which modulation scheme is to be applied to the HS-PDSCH transmission.
- the parameters carried by the HS-SCCH Part 1 message unambiguously specified the codes to be despread and whether the signals were modulated with Quadrature Phase-Shift Keying (QPSK) or 16-QAM (Quadrature Amplitude Modulation).
- QPSK Quadrature Phase-Shift Keying
- 16-QAM Quadrature Amplitude Modulation
- this configuration is performed using higher level signaling. Accordingly, a receiver eavesdropping on HS-SCCH transmissions intended for another UE generally does not know whether that other UE has been configured for 64QAM.
- This signaling of 64QAM configuration for a particular UE does not mean that all subsequent HS-PDSCH transmissions are performed using 64QAM. Rather, it only opens the possibility for a transmission with 64QAM modulation.
- this configuration changes the manner in which the HS-SCCH Part 1 messages are interpreted, an eavesdropping receiver cannot properly interpret the HS-SCCH parameters, even if it properly unmasks and decodes the HS-SCCH Part 1 message. Without the scheduling information carried by the HS-SCCH, of course, an interference-cancelling receiver cannot demodulate and decode interfering HS-PDSCH transmissions to perform subtractive interference cancellation.
- 3GPP TS 25.212 describes the proper formation of the HS-SCCH parameters that indicate the modulation scheme and channelization code set to be used.
- 3GPP TS 25.212 describes the proper formation of the HS-SCCH parameters that indicate the modulation scheme and channelization code set to be used.
- Section 4.6.2.2 of this specification defines a modulation scheme parameter as follows:
- Section 4.6.2.3 of 3GPP TS 25.212 defines the coding for seven channelization code-set bits to be transmitted on the HS-SCCH. These channelization code-set bits need to identify P channelization codes, starting at a code O. The coding of the channelization code-set bits thus depends on P and O, as well as on an HS-SCCH number, in some cases. These parameters are defined in detail by the 3GPP specifications.
- X cc ⁇ s , 7 ⁇ 0 if ⁇ ⁇ 16 ⁇ QAM 1 if ⁇ ⁇ 64 ⁇ QAM .
- the dummy bit xccs,dummy is replaced with a bit that indicates whether 16QAM or 64QAM is used, in the event that the UE is configured for 64QAM and a modulation other than QPSK is scheduled.
- the actual channelization codes used by the HS-PDSCH depend on whether or not 64QAM configuration has been being signaled to the targeted UE. Accordingly, techniques are needed for determining which channelization codes are used for an interfering HS-PDSCH transmission without knowing whether the UE targeted by that transmission has had its 64QAM capability activated by higher layer signaling.
- this is accomplished by measuring the amplitude on each of several possible groups of channelization codes for each of one or more nearby UEs that might be the targets of interfering HS-PDSCH messages. Testing to see whether the amplitude is approximately the same across the codes in a possible combination of channelization codes yields a metric value that indicates whether that particular combination of codes is likely to be transmitted to a given UE. A second metric that detects the most likely modulation for possible groups of channelization codes is also calculated. The two metrics are combined to determine which combination of channelization codes and modulation scheme is most likely being used for addressing a UE in the vicinity of an interference-cancelling receiver.
- the idea behind decoder interference cancellation is to subtract from the input signal a signal generated using decoder output from a prior decoding attempt.
- the decoder output relates to HS-PDSCH from other UEs.
- the output of the decoder produces log-likelihood ratios (LLR), which essentially represent probabilities that a given bit was set to one or zero by the transmitting node.
- LLRs are used to generate probable symbol values as transmitted by the base station.
- the regenerated symbol values are then subjected to the same modulation and scrambling that was performed by the transmitting node, and then the resulting regenerated interfering signal estimate is subtracted from the input signal.
- the regenerated signal from signal regenerator 160 is subtracted from the original input signal, using subtracter 105 , to produce an interference-reduced signal.
- the contribution to the despread signal from the original received signal (for a given code) is denoted y k (i) and the contribution from the subtracted signal is denoted as ⁇ tilde over (y) ⁇ k (i), where i is the symbol index and k the channelization code.
- An equalizer illustrated as a G-RAKE combiner 120 in FIG. 1 , applies equalizer weights to the despread signal to reduce the effects of multipath propagation.
- the equalizer weights, or G-RAKE weights, since the weights are applied after the RAKE, are denoted w.
- the resulting equalized, despread, symbol samples are then demapped, by demapper 130 , to convert them from soft symbols to soft bits.
- the average amplitude d (k) (n s ) over a slot of 160 symbols can be calculated according to:
- the index i enumerates the symbols in time
- n s is the slot number.
- Further filtering of d (k) (n s ) is also possible, both in time and across channelization codes that are known to have been transmitted with the same data amplitude.
- modulation and the power of the HS-PDSCH is the same across all codes destined for a given UE.
- the amplitude estimated in Equation (1) should be the same for all codes used to transmit HS-PDSCH to a given UE.
- An average symbol amplitude estimate is the starting point for the computation of a metric that can be used to determine which of several modulation schemes was most likely used to transmit a series of symbols for a given channelization code or group of channelization codes.
- this metric will be called a “modulation-matching metric.”
- this modulation-matching metric can be used to detect which of the possible modulation schemes, i.e., QPSK, 16QAM, or 64QAM, is most likely being used.
- the modulation-matching metric computation begins with an estimation of the average real and imaginary symbol amplitudes for despread symbols z k (i) obtained from all the channelization codes in the code set of interest. A calculation like that shown in Equation (1) may be used, for example. The resulting amplitude estimate is used to locate where the constellation points are in the I-Q diagram of the constellation map for the corresponding modulation scheme. If the despread symbols come from several channelization codes, the symbols can be assumed to have been transmitted with the same power, and the amplitude estimate may be averaged across the codes.
- the average estimated amplitude for the received despread symbols can be used to scale (i.e., normalize) individual despread symbols to a nominal constellation pattern for a given modulation scheme.
- the smallest of the ratios ⁇ mod,i corresponds to the most likely modulation scheme for the tested samples.
- this smallest ratio can be used to determine the most likely combination of channelization codes and modulation schemes used for one or more interfering signal transmission, and is herein called a modulation-matching metric, denoted by ⁇ mod .
- the value of ⁇ mod,i that corresponds to the hypothesized modulation scheme can be used to evaluate the likelihood that the hypothesis is correct.
- the size of the windows could depend on the measured signal to noise ratio. Larger windows might be used if more noise is present. This is to get better discrimination power from the ratio between elements inside and outside of windows.
- Another metric can be calculated to characterize how equal the power (equivalently, how equal the average amplitude) is for a given set of channelization codes. For the purposes of this disclosure, this metric will be called a “code-power consistency metric.”
- Equation (1) each amplitude per channelization code could be computed as in Equation (1), for example.
- ⁇ i,filt be an averaged (i.e., filtered) value indicating the present best estimate as to whether 64QAM configuration was configured by higher layers for a particular UE over time. This value should be averaged over several scheduling occasions, e.g., about 20. At each occasion, if it is assumed (or estimated) that a transmission for a particular scheduling occasion is done with no 64QAM configuration, then ⁇ i,filt is updated using the value 0. Otherwise, ⁇ i,filt is updated using the value 0.
- the code-power consistency metric is based in part on an assumed setting for the 64QAM configuration parameter, which, as discussed above, is not known to a receiver attempting to demodulate HS-PDSCH transmissions targeted to other UEs.
- the point of the metric function ⁇ ( ⁇ i,filt ,i) is to penalize any selection (assumption) of 64QAM configuration other than the historical value, since this configuration should only change infrequently.
- ⁇ ( ⁇ i,filt ,i ) 100
- ⁇ cc ⁇ d ⁇ d ⁇ + ⁇ ( ⁇ i,filt ,i ), (4)
- i the assumed present 64QAM configuration for this channelization code setup
- ⁇ , ⁇ are empirically-derived weight factors that determine the relative weightings between the distance function for the present observation and the past assumptions for the QAM configuration, as reflected by the metric function ⁇ ( ⁇ i,filt ,i ).
- This expression includes a distance function ( ⁇ d ⁇ d ⁇ ); any of several, such as the Euclidian metric, may be used.
- the normalized L1 norm in particular, is suitable:
- the code-power consistency metric described above can be used to evaluate the likelihood that a particular group of channelization codes is used for a HS-PDSCH transmission to a single UE.
- the code-power consistency metric can be used along with the modulation-matching metric described earlier to determine the combination of channelization codes and modulation schemes that is most likely to have been used to transmit HS-PDSCH to a group of several neighbor UEs.
- FIG. 4 illustrates a general approach that can be implemented in a receiver.
- the UE identifiers for one or more neighboring UEs that might be targeted by interfering transmissions are known.
- all of the possible channelization codes and modulation schemes used for interfering transmissions to each UE must be gathered.
- the identifiers for one or more neighboring UEs are known, it is possible to identify corresponding HS-SCCH messages transmitted from a given cell.
- Each of these HS-SCCH messages is then read to extract the possible modulation schemes and channelization codes for the corresponding UE.
- the interpretation of the HS-SCCH depends on whether the targeted UE has been configured for 64QAM operation. Thus, for every HS-SCCH there are two possible configurations of channelization code-set and modulation scheme for the targeted UE.
- One way to do this is to begin by taking a “cross-section” among all possible channelization code setups. This involves identifying the largest segments of channelization codes within all of the possible groupings such that within each segment it is certain that the modulation and transmitted power is the same. In other words, these segments of channelization codes are the largest possible groupings such that the codes within the group are not split between two or more neighboring wireless terminals.
- ⁇ mod (j) is the modulation-matching metric for a UE indexed by j, calculated using as input the channelization codes in the interval ⁇ k j,1 ,k j,2 ⁇ for a given one of the possible combinations of channelization codes and modulation schemes.
- ⁇ mod (j) There are two possibilities for which value to use for the modulation-matching metric ⁇ mod (j).
- the smallest of these values of ⁇ mod,i corresponds to the most likely modulation scheme for that group of channelization codes, and is used in the subsequent calculations in some embodiments of the invention.
- the modulation-matching metric ⁇ mod,i corresponding to the assumed modulation scheme for that wireless terminal is used, for a given possible combination of channelization codes and modulation schemes.
- the assumed modulation scheme for a given wireless terminal follows from the assumption as to whether 64QAM is configured or not for that wireless terminal, for the given possible combination of channelization codes and modulation schemes. This may differ from one possible combination to another. For example, given two neighboring terminals UE1 and UE2, a first possible combination of channelization codes and modulation schemes may be based on an interpretation of the HS-SCCH scheduling messages that assumes that 64QAM is configured for terminal UE1, but not for UE2.
- Another possible combination may be based on the assumption that 64QAM is configured for terminal UE2, but not for UE1.
- the interpretation of the HS-SCCH message for that terminal indicates a particular modulation scheme—the modulation-matching metric ⁇ mod,i corresponding to that assumed modulation scheme can then be used, in combination with corresponding metrics for other wireless terminals in the combination, to evaluate the likelihood of the combination as a whole.
- modulation-matching metrics and code-power consistency metrics are combined, as shown at block 440 , to yield a combined metric that indicates the likelihood that each combination is the correct one.
- the metrics computed in the previous steps are combined, in a combination metric, ⁇ comb (i), as follows:
- N UE is the number of detected UEs and ⁇ , ⁇ are weight factors, where ⁇ determines how much emphasis (weight) is placed on the modulation-matching metric and ⁇ establishes the emphasis placed on the code-power consistency metrics. Suitable settings for ⁇ , ⁇ are 0.5, although adjustments to these parameters may be determined empirically.
- the combination i with the smallest ⁇ comb (i) value is said to be the correct combination of channelization codes and modulation for the UEs, i.e., the most likely combination used to address UEs in the vicinity of an interference-cancelling receiver.
- FIG. 5 illustrates this more general approach for identifying channelization codes and modulation schemes for interfering signals targeted to neighboring wireless terminals.
- the illustrated method begins with the reading of downlink order data for each of one or more neighboring wireless terminals from a downlink control channel.
- the downlink order data specifies an assignment of one or more channelization codes and a modulation scheme for the corresponding neighboring wireless terminal, where each assignment depending on the downlink order data and an unknown modulation configuration parameter previously sent to the corresponding neighboring wireless terminal.
- the downlink order data is read from an HS-SCCH scheduling message targeted to the neighboring wireless terminal and the unknown modulation configuration parameter is the 64QAM configuration status of the wireless terminal; as discussed earlier, this parameter is signaled via higher-layer control messages and is not readily accessible to an eavesdropping receiver.
- all possible combinations of channelization codes and modulation schemes for all of the neighboring wireless terminals are identified, taking into account possible values for the unknown modulation configuration parameter.
- the possible interpretations for each downlink order data are possible, given the two possible 64QAM configuration states.
- the possible combinations of channelization codes and modulation schemes should also take into account that no two wireless terminals are assigned the same channelization codes. Thus, some combinations of interpretations of the downlink order for the various wireless terminals will result in code allocations that are not possible—these combinations can be eliminated from the set of possible hypotheses for wireless terminal/channelization-code/modulation-scheme arrangements.
- a code-power consistency metric is then calculated for each of the neighboring wireless terminals, as shown at block 530 .
- This code-power consistency metric indicates the probability that all of the channelization codes corresponding to the wireless terminal in a given combination are transmitted with the same power, and is based on despread data samples corresponding to the channelization codes for the respective wireless terminal, given the channelization code allocation for the combination under consideration.
- the code-power consistency metric for each of the neighboring wireless terminals is further based on a filtered average of values for the unknown modulation configuration parameter determined from previous most likely combinations.
- the calculation of the code-power consistency metric for each of the neighboring wireless terminals for each possible combination of channelization codes and modulation schemes includes the following operations. First, a minimal set of channelization code groups is identified, based on the possible combinations of channelization codes and modulation schemes for all of the neighboring wireless terminals. Each of the channelization code groups in this minimal set consists of channelization codes that are not split between two or more neighboring wireless terminals in any of the possible combinations. Next, an average amplitude or power is calculated for each channelization code group, based on despread samples for the corresponding channelization codes.
- the code-power consistency metric is computed, using a distance function that compares the average amplitudes or powers for each channelization code group for the neighboring wireless terminal to an average amplitude or power for all channelization code groups for the neighboring wireless terminal. Equations (3)-(5) above provide one example of how to calculate this code-power consistency metric.
- the code-power consistency metric is computed by calculating a weighted average of the distance function and a filtered average of values for the unknown modulation configuration parameter determined from previous most likely combinations.
- a modulation-matching metric is calculated for each of the neighboring wireless terminals, for each of the possible combinations. Again, this modulation-matching metric is based on received despread data samples corresponding to the channelization codes. The modulation-matching metric indicates how closely the received symbols match a constellation pattern for one of the possible modulation schemes.
- the modulation-matching metric for each of the neighboring wireless terminals for a given possible combination is calculated, for each neighboring wireless terminal and its corresponding channelization codes, by comparing despread samples for the corresponding channelization codes to an assumed map of constellation points and calculating a fraction of despread samples that fall outside defined windows centered on each constellation point.
- the modulation-matching metric corresponds to the most likely modulation scheme for the wireless terminal, given a possible allocation of channelization codes. In other cases, however, the modulation-matching metric for each of the neighboring wireless terminals is calculated based on assumed modulation schemes for each of the neighboring wireless terminals, where the assumed modulation schemes are determined from the current assumed values for the unknown modulation configuration parameter.
- a most likely one of the possible combinations of channelization codes and modulation schemes is identified, as shown at block 550 . This is done using a weighted sum of the code-power consistency metrics and modulation-matching metrics for each possible combination. While an example weighting for an HSDPA system is suggested in the detailed discussion above, it will be appreciated that optimal weights for a given system and/or signal scenario may be determined through empirical testing and/or through system simulation.
- the technique illustrated in FIG. 5 is of particular use in an interference-cancelling receiver, as the channelization code and modulation scheme information can be used to demodulate traffic data transmitted to the neighboring terminals, e.g., HSDPA transmissions in an HSDPA system. Accordingly, the operations illustrated in FIG. 5 may in some cases be followed by the forming of a reconstructed estimate of interfering signals corresponding to one or more of the neighboring wireless terminals, based on corresponding channelization codes and modulation schemes determined from the most likely one of the possible combinations. Interference cancellation can then be using the reconstructed estimate of the interfering signal.
- a modulation configuration detection circuit can be configured to carry out one or more of these techniques.
- This modulation configuration detection circuit might be used, for example, to augment an interference-cancelling receiver, such as the receiver illustrated in FIG. 1 , thus enabling the receiver to regenerate and cancel interfering signals targeted to neighboring wireless terminals.
- FIG. 6 illustrates functional components of an example modulation configuration detection circuit 600 adapted for HSDPA operation. A similar circuit could be applied to other wireless system contexts.
- Circuit 600 includes an HS-SCCH message decoder 610 , which reads and interprets downlink assignment messages for neighboring wireless terminals.
- the downlink order data included in these messages specify an assignment of one or more channelization codes and a modulation scheme for the targeted wireless terminal, but the proper interpretation of the order data depends on whether or not the wireless terminal is configured for 64QAM operation, which is normally unknown to other receivers.
- Circuit 600 further includes a hypothesis generator 620 , which identifies all possible combinations of channelization codes and modulation schemes for all of the neighboring wireless terminals, taking into account possible values for the unknown modulation configuration parameter and that no two wireless terminals are assigned the same channelization codes.
- Metric generator 630 calculates two metrics for each of the neighboring wireless terminals, for each possible combination: a code-power consistency metric and a modulation-matching metric. These metrics are based on despread data samples corresponding to the channelization codes for each wireless terminal, for each possible combination of channelization code and modulation scheme allocations. Detailed examples of these calculations were given above.
- channelization code and modulation identifier 640 identifies a most likely one of the possible combinations, using a weighted sum of the code-power consistency metrics and modulation-matching metrics for each possible combination. This information is supplied to demodulation circuits so that the corresponding HS-PDSCH transmissions to the neighboring wireless terminals can be demodulated, regenerated, and cancelled from the received signal.
- the several functional blocks of circuit 600 may be implemented using digital logic and/or one or more microcontrollers, microprocessors, or other digital hardware. In some embodiments, several or all of the various functions of receiver circuit 600 may be implemented together, such as in a single application-specific integrated circuit (ASIC), or in two or more separate devices with appropriate hardware and/or software interfaces between them.
- ASIC application-specific integrated circuit
- Several of the functional blocks of receiver circuit 600 may be implemented on a processor shared with other functional components of a wireless terminal, for example, such as one or more of the components illustrated in FIG. 1 .
- processors or “controller” as used herein does not exclusively refer to hardware capable of executing software and may implicitly include, without limitation, digital signal processor (DSP) hardware, read-only memory (ROM) for storing software, random-access memory for storing software and/or program or application data, and non-volatile memory.
- DSP digital signal processor
- ROM read-only memory
- RAM random-access memory
- non-volatile memory non-volatile memory
- FIG. 7 illustrates one example of a processing circuit 710 adapted to carry out the functions of one or more of the functional blocks of receiver circuit 600 .
- Processing circuit 710 includes a central-processing unit (CPU) 740 , which may comprise one or more microprocessors, microcontrollers, and/or the like, coupled to memory unit 750 .
- Memory unit 750 which may comprise one or several types of memory such as RAM, ROM, Flash, optical storage devices, magnetic storage devices, and the like, stores computer program instructions 760 for execution by CPU 740 , and stores program data 755 .
- Program instructions 760 include instructions for carrying out one or more of the techniques described above.
- program instructions 760 may include, in several embodiments, computer program instructions for identifying channelization codes and modulation schemes for interfering signals targeted to neighboring wireless terminals, using one of the detailed techniques described above or variants thereof.
- the processing circuit 710 of FIG. 7 may be further configured, in some embodiments, to carry out some or all of the functions of one or more of the other functional blocks of FIG. 1 , such as decoder 140 , soft mapper 150 , signal regenerator 160 , and so on. In some cases some or all of these functions may be carried out on separate processing circuits, which may or may not have similar structures. It will be appreciated, of course, that several of the functions of receiver circuit 100 may be better suited for implementation in specialized digital hardware. For example, hardware implementations of high-speed correlator arrays suitable for implementing RAKE despreader 110 are well known.
Abstract
Description
Note that “otherwise” refers to 16QAM modulation if the targeted UE is not configured for 64QAM operation. If the targeted UE is configured for 64QAM, on the other hand, then “otherwise” includes both 16QAM and 64QAM as possibilities.
xccs,1,xccs,2,xccs,3=min(P−1,15−P)
If 64QAM is not configured for the UE, or if 64QAM is configured and the modulation scheme parameter xms,1 is equal to 0, then the last four bits are given by:
xccs,4,xccs,5,xccs,6,xccs,7=|O−1−└P/8┘*15|.
Otherwise (i.e., if 64QAM is configured for the UE and xms,1=1), then:
P and O shall fulfil |O−1−└P/8┘*15|mod 2=(HS-SCCH number) mod 2,
and:
xccs,4,xccs,5,xccs,6,xccs,dummy=|O−1−└P/8┘*15|,
where xccs,dummy is a dummy bit that is not transmitted on HS-SCCH. Furthermore, if 64QAM is configured for the UE and xms,1=1, then:
In effect, the dummy bit xccs,dummy is replaced with a bit that indicates whether 16QAM or 64QAM is used, in the event that the UE is configured for 64QAM and a modulation other than QPSK is scheduled.
Here, the index i enumerates the symbols in time, and ns is the slot number. Further filtering of d(k)(ns) is also possible, both in time and across channelization codes that are known to have been transmitted with the same data amplitude. In a WCDMA system, modulation and the power of the HS-PDSCH is the same across all codes destined for a given UE. Thus, the amplitude estimated in Equation (1) should be the same for all codes used to transmit HS-PDSCH to a given UE.
Then, define the vector
ƒ(μi,filt ,i)=100|μi,filt −i|, (3)
where the filtered value μi,filt is compared with the assumed present 64QAM configuration i, where i takes a
μcc =α∥d−
where i is the assumed present 64QAM configuration for this channelization code setup and α,β are empirically-derived weight factors that determine the relative weightings between the distance function for the present observation and the past assumptions for the QAM configuration, as reflected by the metric function ƒ(μi,filt ,i). This expression includes a distance function (∥d−
A suitable value for both α,β is 0.5. These values can be adjusted, however, e.g., based on the results of empirical testing in various conditions or based on changes in the make-up of the metric function metric function ƒ(μi,filt ,i)
Here, NUE is the number of detected UEs and α,β are weight factors, where α determines how much emphasis (weight) is placed on the modulation-matching metric and β establishes the emphasis placed on the code-power consistency metrics. Suitable settings for α,β are 0.5, although adjustments to these parameters may be determined empirically. The combination i with the smallest μcomb(i) value is said to be the correct combination of channelization codes and modulation for the UEs, i.e., the most likely combination used to address UEs in the vicinity of an interference-cancelling receiver.
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CN105357696B (en) * | 2015-10-29 | 2019-02-15 | 江苏鑫软图无线技术股份有限公司 | A kind of improved PUSCH signal-to-noise ratio measuring method of TDD-LTE system |
DE102015122458A1 (en) | 2015-12-21 | 2017-06-22 | Intel IP Corporation | COMMUNICATION DEVICE AND METHOD FOR SIGNAL DETERMINATION |
US10708095B2 (en) * | 2018-09-13 | 2020-07-07 | Viasat, Inc. | Generating metrics from samples of a received signal in a communications receiver supporting multiple operating modes |
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